The present invention further relates to a novel method for making the agglomerate support composition and supported catalysts derived therefrom disclosed in the above-identified related patent applications.
It is well known that catalysts supported on a silica gel support are useful in the polymerization of olefins. The nature of the resulting polymer is highly dependent upon the catalyst, so that variations in the characteristics of the catalyst will cause variations in, for example, the molecular weight, melt index, bulk density, particle shape, particle size, particle size distribution and reaction temperature which may be employed to effect polymerization. Furthermore, the nature of the catalyst and its performance is highly dependent upon the properties of the material used to support the catalyst. The properties of the support are in turn dependent on its method of manufacture.
Using different support materials with different physical characteristics is known in the art. Agglomerated catalytic support materials and catalysts have been prepared by a variety of methods.
Some methods involve agglomeration of particles from various types of dispersions, e.g. colloidal sols, through various mechanisms, e.g. through gellation, recovering the agglomerate, and drying. Other methods employ spray drying to cause agglomeration.
For example, the following U.S. patents disclose various non-spray drying techniques for making silica containing supports: U.S. Pat. Nos. 3,887,494; 4,076,651; 4,657,880; 4,704,374; 4,849,390; 4,902,666; and 5,108,975.
Sano et al., U.S. Pat. No. 4,849,390 disclose supported titanium or vanadium-containing catalysts useful for polymerizing olefins which employ a silicon and/or aluminum oxide carrier. The carrier must have a specified sphericality, average pore size (180-250 angstroms), pore size distribution (60% or more of the pores have a diameter of 100 to 300 angstroms), and breakage resistance. The breakage resistance is quantified by subjecting the particles to ultrasonic waves for two hours and measuring the resulting particle size distribution. The carrier is desirably breakage resistant if .gtoreq.50% of the particles have a particle size between 50-150 microns.
The following U.S. patents disclose spray dried silica or silica containing supports which do not employ a premilling step: U.S. Pat. Nos. 3,607,777; 3,965,042; 4,070,286; 4,105,426; 4,131,542; 4,228,260; 4,272,409; 4,460,700; 4,548,912; 4,677,084; 5,128,114; 5,302,566; 5,352,645; 5,403,809, and 5,569,634.
A number of the above patents assigned to E. I. DuPont de Nemours and Company disclose attrition resistant spray dried microspheroid agglomerates derived from colloidal particles.
More specifically, Iler et al. U.S. Pat. Nos. 4,105,426 and 4,131,542 disclose macroporous microspheroids derived from a silica sol comprising a mixture of large colloidal silica particles (average particle size (APS) 0.1 to 1 micron) and small colloidal silica particles (APS 1 to 10 nanometers) which are spray dried and sintered to convert the small colloidal silica particles to mechanically strong non-porous amorphous silica cement. The large colloidal particles of the intermediate microspheroidal powder prior to sintering are held together by the small colloidal particles. The resulting microspheroids have an average pore diameter of 0.05 to 0.5 microns.
In contrast, the microspheroids made by the method of the present invention are derived primarily from non-colloidal sized particles.
Bergna et al., U.S. Pat. No. 4,131,542 spray dries a silica sol to produce porous micrograms containing constituent particles in the 5 to 80 nanometer range which are then sintered to improve attrition resistance.
Schwartz, U.S. Pat. No. 5,128,114 (see also U.S. Pat. No. 5,352,645) discloses high strength, non-agglomerated porous microspheres of silica prepared by spray drying a mixture of an aqueous silica sol and an ammonium citrate or urea additive. The additive counteracts the tendency of the silica aquasol droplets to form an impervious crust during spray drying which, in turn, prevents the droplets from rupturing. The colloidal particles in the silica aquasol range from 5 to 100 nanometers.
Spencer et al., PCT Pub. No. WO96/05236 discloses magnesium halide supported on microspheroidal agglomerates of silica subparticles having controlled hydroxyl content. The agglomerates are characterized as possessing a void fraction of from 5 to 30 percent from cross-sectional analysis of the agglomerate by a scanning electron micrograph. However, from the figures of this publication, it can be seen that very little of the void space penetrates to the surface of the agglomerate. The only spray drying method disclosed for preparing such an agglomerate is an incorporation by reference to Winyall et al., U.S. Pat. No. 3,607,777. The preparative procedures for the samples used to generate FIGS. 1 and 2 are not disclosed, nor are the preparative procedures for the samples of Example 33. All of the agglomerated supports employed in the examples were purchased from Grace Davison under the tradename SYLOPOL.RTM., and no preparative procedure is disclosed. Specific suitable supports mentioned are designated SYLOPOL.RTM. 948, SYLOPOL.RTM. 956, SYLOPOL.RTM. 2104, and SYLOPOL.RTM. 2212, available from Grace Davison.
Winyall et al., U.S. Pat. No. 3,607,777, discloses a preparative method which specifically avoids any milling whatsoever of the silica gel.
Sato et al. Japanese Patent Pub. 61-174103 discloses a process for producing porous spherical fine powders having an average particle size of 1 to 20 microns by spray drying a mixture of a colloidal oxide sol (10-95 parts) and inorganic oxide gel (5-90 parts). However, while the average particle size of the colloidal sol particles are less than 2,500 Angstroms, the average particle size of the gel is also in the colloidal range of less than 1 micron.
Miller et al., U.S. Pat. No. 5,569,634 discloses the preparation of porous bodies suitable for use as a catalyst support but primarily as a biocarrier, which bodies are derived from the extrusion, pelletization, balling, or granulating of ultimate particles and optional binder. The ultimate particles comprise inorganic oxide particles (which must contain at least some zeolite) of 1-1000 microns. The preferred inorganic oxide is clay (i.e., natural or synthetic hydrated aluminosilicates). The binder for the ultimate particles can be silica. The ultimate particles can be formed by spray drying a mixture of clay, zeolite, and optional binder.
The ultimate particles must possess a requisite physical integrity or they will be crushed, deformed, or attrited during the formation of the porous body. A Davison Index for attrition is disclosed which is similar to the AQI test (described hereinafter in greater detail), but much more severe, e.g., it uses an air flow rate of 21 liters per minute (AQI flow rate=9 liters/min.), for 60 minutes (AQI test=30 min.). Moreover, the Davison Index test uses a 0-20 micron base line, rather than the 0-16 micron base line of the AQI test. Suitable Davison Index values for the ultimate particle are disclosed to be 70 or less. Thus, the ultimate particle is merely an intermediate in the formation of the porous body, and the morphology of the ultimate particle is not disclosed. The use of silica gel or the milling thereof to prepare the inorganic oxides for spray drying is not disclosed.
The following patents disclose spray drying of silica supports and employ premilling of a silica gel: U.S. Pat. Nos. 5,589,150 and 5,604,170; PCT Publication Nos. WO096/34062 and WO 93/23438; and German Patent Application No. DE 41 332 30.4.
More specifically, Kano et al., U.S. Pat. No. 5,589,150 discloses a method for preparing spherular silica gel particles wherein a hydrosol is allowed to congeal to a hydrogel. This hydrogel is filtered, slurried and rinsed, and mixed with demineralized water, the filtrate adjusted to a pH of 1-10 with ammonia, and the slurry thermally treated for 1 to 50 hours at 50 to 200.degree. C. The resulting thermally treated silica hydrogel is then filtered and coarsely ground using an impact mill to a particle diameter of 100-200 microns. The coarsely ground particles are then slurried in water to a predetermined moisture content such that the weight ratio of water:silica hydrogel in the slurry is 0.2:1 to 1.5:1. Control of the moisture content is deemed critical, inter-alia, to obtain sufficiently high particle strength. The resulting slurry is then wet milled to reduce the particle size to between 1 and 50 microns. The wet milled slurry is then spray dried at various different solids and pH combinations reported in the examples, i.e., a pH of 8.5 and moisture ratios of 0.75 to 1.33 for embodiments 1-3, and a pH of 2.0 and moisture ratios of 0.35 to 0.45 for embodiments 4-6.
However, Kano et al. fail to disclose a procedure involving sequential dry milling and wet milling of a powder. Moreover, it is clear that Kano et al. seek to form agglomerates having a high particle strength in contrast to the presently claimed invention which seeks to form agglomerates having a sufficiently low particle strength, expressed by AQI, that they will break apart during polymerization. Kano et al. also fail to disclose anything about the surface texture and void space of the agglomerate. Without wishing to be bound by any particular theory, such factors are believed to significantly influence the degree of deposition of the catalytic components within the agglomerate, as described hereinafter in greater detail.
Sano et al. U.S. Pat. No. 5,604,170 discloses the use of an oxide support of silicon or aluminum having 5 different property types of average particle size (20-150 microns), specific surface area (150-600 m.sup.2 /g), pore volume distribution (0.3 to 2.0 cm.sup.3 /g for 18 to 1000 Angstrom pore radius) specific gravity (.gtoreq.0.32), and degree of resistance to ultrasonic disintegration to 50 microns or smaller particle size, of not more than 30% for samples classified between 53 and 75 microns. Only wet milling of coarsely pulverized particles (using a hammer mill) is disclosed.
Belligoi et al. PCT Publication No. WO96/34062 discloses aggregated silica gel made by spray drying a mixture of micronized silica gel and a binding agent selected from phyllosilicate, pyrogenic silicon dioxide and water soluble organic polymers. The resulting product is employed as a matting agent or blocking agent and not as a catalyst support.
In contrast, the preferred embodiments of the present invention rely on minor amounts of colloidal components of sequentially milled silica gel as the binder for non-colloidal constituents of the agglomerate. Any organic polymer would be destroyed upon calcination of the support for use as a polymerization catalyst. Belligoi et al. do not employ calcination. More importantly, Belligoi et al. seek to form a stable aggregate to withstand shear forces during dispersion of the matting agent into paint (pg. 4, line 26 et seq.). This stability is accomplished with the binding agent which is intended to exert a much greater binding effect than the colloidal constituents, when present, of the milled particles of the present invention wherein the binding effect is merely to hold the agglomerate together for handling. In the present invention, upon use as a polymerization catalyst, the binder must release the constituent particles and permit the agglomerate to break apart. Belligoi et al. also fail to disclose sequential dry milling and wet milling steps. However, they do employ SYLOID.RTM. 244 which, although not known, is a milled powder.
Marsden, PCT Publication No. WO093/23438 discloses porous microspherical cogel particles comprising silica and at least one other metal oxide derived by spray drying from a liquid medium comprising at least 90 weight percent organic liquid. While the cogel is wet milled down to a 1 to 60 micron average particle size, the wet milling is performed in an organic medium. No dry milling of a powder is disclosed.
U.S. Pat. No. 5,552,361 discloses a process for making aluminum phosphate microspherical particles with a bimodal pore size distribution. An aluminum phosphate hydrogel is wet milled to a particle size of less than 10 microns and the slurry spray dried at a pH of 3 to 7 and a solids content of 10-13 weight percent to produce agglomerates having a particle size of 10 to 250 microns.
DE 41 322 30.4 discloses a spherical silica gel made by the sol-gel process for use as a matting agent in paints. The sol-gel is crushed without water loss to about a 10 micron median particle size, and the crushed silicon dioxide resuspended in water for spray drying. Thus, the disclosed process does not employ a dry milling of powder step. The resulting material has increased abrasion resistance. Neither the AQI nor the pH of the spray drying are disclosed.
The process described in related U.S. patent application Ser. No. 878,476 filed Jun. 19, 1997, involves mixing a dry milled powder with a wet milled powder. In contrast, the presently claimed invention involves sequentially dry milling and then wet milling the same sample. This process is easier to conduct and still achieves the desired morphological properties and low AQI.
Thus, there has been a continuing search for methods for making catalyst supports which are easy to handle and which improve the catalyst performance in polymerizing olefins. The present invention was developed in response to this search.